Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A method of generating random access preambles includes receiving
information on a source logical index and generating random access
preambles in the order of increasing cyclic shift from root ZC sequences
with the consecutive logical indexes from the beginning of the source
logical index until a predetermined number of the random access preambles
are found, wherein the consecutive logical indexes are mapped to root
indexes of the root ZC sequences.

Claims:

1. A method of generating logical indexes of root Zadoff-Chu (ZC)
sequences, the method comprising:dividing a plurality of root indexes of
root ZC sequences into one or more subgroups according to predetermined
cyclic shift parameters, a subgroup including at least one root index of
a root ZC sequence; andmapping the root indexes of the root ZC sequences
in the subgroup to consecutive logical indexes.

2. The method of claim 1, wherein a root ZC sequence has zero correlation
zones of length (the value of the cyclic shift parameter of the root ZC
sequence-1).

3. The method of claim 1, further comprising:ordering the root indexes of
root ZC sequences in a subgroup according to a metric before mapping to
the logical indexes.

4. The method of claim 3, wherein the metric is cubic metric (CM).

5. The method of claim 1, further comprising:performing cyclic shifts of a
root ZC sequence with a value of cyclic shift, wherein the value of
cyclic shift is obtained using a cyclic shift parameter of the root ZC
sequence and a Doppler shift of detection stage.

6. The method of claim 5, wherein the cyclic shift parameter of the root
ZC sequence is smaller than or equal to the predetermined cyclic shift
parameter of the subgroup of the root ZC sequence.

7. The method of claim 5, wherein the value of cyclic shift of the root ZC
sequence is greater than the cyclic shift parameter of the root ZC
sequence.

9. The method of claim 1, further comprising:ordering the subgroups
according to predetermined cyclic shift parameters.

10. The method of claim 1, wherein the last logical index for a first
subgroup is consecutive to the first logical index for a second subgroup,
the second subgroup being consecutive to the first subgroup.

11. A method of performing random access procedure in a wireless
communication system, the method comprising:selecting a random access
preamble from a plurality of random access preambles, the plurality of
random access preambles being generated from available cyclic shifts of
root ZC sequences with consecutive logical indexes, wherein the
consecutive logical indexes are mapped to root indexes of the root ZC
sequences;transmitting the selected random access preamble; andreceiving
a random access response including the identifier of the selected random
access preamble.

12. The method of claim 11, wherein sum of two root indexes of root ZC
sequences corresponding to two consecutive logical indexes is equal to
the length of a root ZC sequence.

13. The method of claim 11, wherein the random access response on a
downlink shard channel (DL-SCH) is addressed to a random access
identifier on a physical downlink control channel (PDCCH).

14. The method of claim 11, further comprising:receiving a logical index
and a cyclic shift parameter from a base station to generate the random
access preambles, wherein the cyclic shift parameter is used to obtain
the value of cyclic shift.

15. A method of performing random access procedure in a wireless
communication system, the method comprising:transmitting a source logical
index for generating a plurality of random access preambles and a
predetermined cyclic shift parameter;receiving a random access preamble
selected from the plurality of random access preambles, the plurality of
random access preambles being generated from available cyclic shifts of
root ZC sequences with the source logical index and at least one
consecutive logical index of the source logical index; andtransmitting a
random access response including the identifier of the random access
preamble.

16. The method of claim 15, wherein the source logical index is
broadcasted as part of system information.

17. The method of claim 15, wherein sum of two root indexes of root ZC
sequences corresponding to two consecutive logical indexes is equal to
the length of a root ZC sequence.

18. The method of claim 15, further comprising:receiving a cyclic shift
parameter, wherein the value of cyclic shift is obtained using the cyclic
shift parameter.

19. A method of generating random access preambles, the method
comprising:generating random access preambles in the order of increasing
cyclic shift from a first root ZC sequence with a first root index mapped
to a first logical index; andgenerating additional random access
preambles in the order of increasing cyclic shift from a second root ZC
sequence with a second root index mapped to a second logical index when a
predetermined number of random access preambles cannot be generated from
the first root ZC sequence, the second logical index being consecutive to
the first logical index.

20. The method of claim 19, further comprising:receiving the first logical
index from a base station.

21. The method of claim 19, wherein the predetermined number of random
access preambles is 64.

22. The method of claim 19, further comprising:receiving information on a
cyclic shift parameter, wherein the value of cyclic shift is obtained
using the cyclic shift parameter.

23. The method of claim 19, further comprising:selecting a random access
preamble from the random access preambles and the additional random
access preambles; andtransmitting the selected random access preamble.

24. A method of generating random access preambles, the method
comprising:receiving information on a source logical index; andgenerating
random access preambles in the order of increasing cyclic shift from root
ZC sequences with the consecutive logical indexes from the beginning of
the source logical index until a predetermined number of the random
access preambles are found, wherein the consecutive logical indexes are
mapped to root indexes of the root ZC sequences.

25. The method of claim 24, wherein the random access preambles are
generated in the order of increasing cyclic shift from a root ZC
sequence.

26. The method of claim 25, further comprising:receiving information on a
cyclic shift parameter, wherein the value of cyclic shift is obtained
using the cyclic shift parameter.

[0003]The present invention relates to wireless communication and, in
particular, to a method of generating random access preambles in a
wireless communication system.

[0004]2. Related Art

[0005]The 3GPP (3rd Generation Partnership Project) mobile communication
system based on WCDMA (Wideband Code Division Multiple Access) radio
access technologies is widely deployed all over the world. An HSDPA (High
Speed Downlink Packet Access), which could be defined as the first
evaluation phase of the WCDMA, provides radio access technologies that
are highly competitive in the mid-term future. However, because radio
access technologies are being constantly advanced to meet the increasing
demands and expectations of users and providers, new technological
evolution is required in the 3GPP to ensure competitiveness in the
future.

[0006]One of the systems that are considered to follow the 3rd generation
systems is an OFDM (Orthogonal Frequency Division Multiplexing) system
that attenuates inter-symbol interference (ISI) with low complexity. In
the OFDM, serially inputted data symbols are converted into the N number
of parallel data symbols, transmitted on the N number of orthogonal
subcarriers. The subcarriers maintain orthogonality in frequency domain.
Respective orthogonal channels experience mutually independent frequency
selective fading, and when the interval between symbols is long enough,
ISI can be canceled. An OFDMA (Orthogonal Frequency Division Multiple
Access) refers to a multiple access method using the OFDM as modulation
scheme. In the OFDMA, the frequency resources, namely, the subcarriers,
are provided to each user. In this case, because each frequency resource
is independently provided to a plurality of users, the frequency
resources do not overlap with each other. Namely, the frequency resources
are allocated to the users exclusively.

[0007]In order to transmit or receive a data packet, control information
needs to be transmitted. For example, uplink control information includes
ACK (Acknowledgement)/NACK (Negative-Acknowledgement) signals indicating
successful transmission of downlink data, a CQI (Channel Quality
Indicator) indicating quality of a downlink channel, a PMI (Precoding
Matrix Index), an RI (Rank Indicator), etc. In addition, a random access
preamble needs to be transmitted to perform a random access procedure.

[0008]A sequence is commonly used to transmit the uplink control
information or the random access preamble. The sequence is transmitted in
the form of a spreading code, a user equipment identifier, or a signature
via a control channel or a random access channel.

[0009]FIG. 1 is an exemplary view showing a method for performing a random
access procedure in a WCDMA system. The random access procedure is
performed to allow a user equipment to acquire uplink synchronization
with a network or acquire uplink radio resources for transmitting uplink
data.

[0010]Referring to FIG. 1, a user equipment transmits a preamble via a
PRACH (Physical Random Access Channel) which is an uplink physical
channel. The preamble is transmitted during the access slot of 1.33 ms.
The preamble is randomly selected from sixteen preambles.

[0011]Upon receiving the preamble from the user equipment, a base station
transmits a response via an AICH (Acquisition Indicator Channel) which is
a downlink physical channel. The base station transmits an
acknowledgement (ACK) or a negative acknowledgement (NACK) to the user
equipment via the AICH. If the user equipment receives ACK, the user
equipment transmits a message having a length of 10 ms or 20 ms by using
an OVSF (Orthogonal Variable Spreading Factor) code corresponding to the
preamble. If the user equipment receives NACK, the user equipment
transmits the preamble again in a suitable time. If the user equipment
fails to receive a response corresponding to the previously transmitted
preamble, the user equipment transmits a new preamble with power level
higher than that of the previous preamble after a determined access slot.

[0012]The user equipment acquire information on sixteen preambles (namely,
sequences), and uses one selected from the sixteen preambles as a
preamble in the random access procedure. If the base station informs the
user equipment of information regarding every available sequence,
signaling overhead may be increased. So, generally, the base station
previously designates sets of sequences and transfers an index of the
sets of sequences to the sixteen preambles. For this purpose, the user
equipment and the base station should store the sets of sequences
according to the index in their buffer, respectively. This may be
burdensome if the number of sequences belonging to the sequence sets is
increased or the number of sets of sequences is increased.

[0013]In order to enhance performance of data detection in a receiver and
increase capability, correlation or CM (Cubic Metric) characteristics of
the sequences should be guaranteed to a degree. This means that the
sequences belonging to the sequence sets used for the random access
procedure should have correlation or CM characteristics guaranteed by
more than a certain level. In particular, a sequence used for a high
speed environment in which the user equipment is moved by a speed of 30
km/h or faster and a sequence used for a low speed environment need to be
separately used in order to guarantee sequence characteristics in
consideration of Doppler effect.

[0014]A method is sought for guaranteeing the characteristics of sequences
used for transmission of the uplink control information with smaller
amount of signaling overhead.

[0018]In an aspect, a method of generating logical indexes of root
Zadoff-Chu (ZC) sequences is provided. The method includes dividing a
plurality of root indexes of root ZC sequences into one or more subgroups
according to predetermined cyclic shift parameters, a subgroup including
at least one root index of a root ZC sequence and mapping the root
indexes of the root ZC sequences in the subgroup to consecutive logical
indexes.

[0019]In another aspect, a method of performing random access procedure in
a wireless communication system is provided. The method includes
selecting a random access preamble from a plurality of random access
preambles, the plurality of random access preambles being generated from
available cyclic shifts of root ZC sequences with consecutive logical
indexes, wherein the consecutive logical indexes are mapped to root
indexes of the root ZC sequences, transmitting the selected random access
preamble and receiving a random access response including the identifier
of the selected random access preamble.

[0020]In still another aspect, a method of performing random access
procedure in a wireless communication system is provided. The method
includes transmitting a source logical index for generating a plurality
of random access preambles and a predetermined cyclic shift parameter,
receiving a random access preamble selected from the plurality of random
access preambles, the plurality of random access preambles being
generated from available cyclic shifts of root ZC sequences with the
source logical index and at least one consecutive logical index of the
source logical index and transmitting a random access response including
the identifier of the random access preamble.

[0021]In still another aspect, a method of generating random access
preambles is provided. The method includes generating random access
preambles in the order of increasing cyclic shift from a first root ZC
sequence with a first root index mapped to a first logical index and
generating additional random access preambles in the order of increasing
cyclic shift from a second root ZC sequence with a second root index
mapped to a second logical index when a predetermined number of random
access preambles cannot be generated from the first root ZC sequence, the
second logical index being consecutive to the first logical index.

[0022]In still another aspect, a method of generating random access
preambles includes receiving information on a source logical index and
generating random access preambles in the order of increasing cyclic
shift from root ZC sequences with the consecutive logical indexes from
the beginning of the source logical index until a predetermined number of
the random access preambles are found, wherein the consecutive logical
indexes are mapped to root indexes of the root ZC sequences.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is an exemplary view showing a method of performing a random
access procedure in a WCDMA system.

[0025]FIG. 3 is a flow chart illustrating the process of a method of
generating sequences according to one exemplary embodiment of the present
invention.

[0026]FIG. 4 is a graph showing CM (Cubic Metric) characteristics and
maximum supportable cell radius characteristics according to physical
root indexes according to one exemplary embodiment of the present
invention.

[0027]FIG. 5 is a graph showing CM characteristics and maximum supportable
cell radius characteristics according to logical root indexes according
to one exemplary embodiment of the present invention.

[0028]FIG. 6 is a graph showing CM characteristics and maximum supportable
cell radius characteristics according to logical root indexes according
to another exemplary embodiment of the present invention.

[0029]FIGS. 7 to 14 are graphs showing CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to still another exemplary embodiment of the present invention.

[0030]FIG. 15 is a graph showing the number of restricted cyclic shifts
that can be used per logical root index according to Ncs with respect to
CM mapping according to one exemplary embodiment of the present
invention.

[0031]FIG. 16 is a graph showing the number of restricted cyclic shifts
that can be used per logical root index according to Ncs with respect to
maximum supportable cell size mapping according to one exemplary
embodiment of the present invention.

[0032]FIG. 17 is a graph showing the number of restricted cyclic shifts
that can be used per logical root index according to Ncs with respect to
hybrid mapping according to one exemplary embodiment of the present
invention.

[0033]FIG. 18 is a graph showing examples of logical root indexes
allocated to cells with respect to CM mapping according to one exemplary
embodiment of the present invention.

[0034]FIG. 19 is a graph showing examples of logical root indexes
allocated to cells with respect to maximum supportable cell size mapping
according to one exemplary embodiment of the present invention.

[0035]FIG. 20 is a graph showing examples of logical root indexes
allocated to cells with respect to maximum supportable cell size mapping
according to one exemplary embodiment of the present invention.

[0036]FIG. 21 is a view illustrating a method of searching logical root
indexes according to CM characteristics according to one exemplary
embodiment of the present invention.

[0037]FIG. 22 is a view illustrating a method of searching logical root
indexes according to CM characteristics according to another exemplary
embodiment of the present invention.

[0038]FIG. 23 is a view illustrating a method of searching logical root
indexes according to CM characteristics according to still another
exemplary embodiment of the present invention.

[0039]FIG. 24 is a graph showing CM characteristics according to physical
root indexes according to one exemplary embodiment of the present
invention.

[0040]FIG. 25 is a graph showing CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to another exemplary embodiment of the present invention.

[0041]FIG. 26 is a graph showing CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to another exemplary embodiment of the present invention.

[0042]FIG. 27 is a graph showing a process of grouping CM ordering into
two groups.

[0043]FIG. 28 is a graph showing a process of grouping indexes ordered
according to maximum supportable Ncs characteristics into Ncs groups in
each group.

[0044]FIG. 29 is a graph showing a process of ordering indexes according
to the CM characteristics in each Ncs group.

[0045]FIG. 30 is a flow chart illustrating the random access procedure
according to one exemplary embodiment of the present invention.

[0046]FIG. 31 is a schematic block diagram of elements of a user equipment
to which the exemplary embodiments are applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0047]FIG. 2 illustrates a wireless communication system. The wireless
communication system can widely be deployed to provide various
communication services such as voice and packet data, etc.

[0048]Referring to FIG. 2, a wireless communication system includes a user
equipment (UE) 10 and a base station (BS) 20. The UE 10, which may be
fixed or mobile, may be called other terms such as an MS (Mobile
Station), a UT (User Terminal), an SS (Subscriber Station), a wireless
device, and so on. The BS 20 refers to a fixed station that communicates
with the UE 10, and may be also called a Node-B, a BTS (Base Transceiver
System), an AP (Access Point), and so on. One or more cells may exist in
a BS 20.

[0049]Hereinafter, downlink refers to communication from the BS 20 to the
UE 10, and uplink refers to communication from the UE 10 to the BS 20. In
the downlink, a transmitter may be a part of the BS 20, and a receiver
may be a part of the UE 10. In the uplink, a transmitter may be a part of
the UE 10 and a receiver may be a part of the BS 20.

[0050]There is no limitation in multiple access techniques applied to the
wireless communication system. For example, various multiple access
techniques such as CDMA (Code Division Multiple Access), TDMA (Time
Division Multiple Access), FDMA (Frequency Division Multiple Access),
SC-FDMA (Single Carrier-FDMA), and OFDMA (Orthogonal Frequency Division
Multiple Access) can be used. For clarification, the OFDMA-based wireless
communication system will now be described hereinafter.

[0051]The OFDM uses a plurality of orthogonal subcarriers. The OFDM uses
orthogonality between IFFT (Inverse Fast Fourier Transform) and FFT (Fast
Fourier Transform). A transmitter performs IFFT on data and transmits the
same. A receiver performs FFT on a received signal to restore the
original data. The transmitter uses IFFT to combine multiple subcarriers
and the receiver uses corresponding FFT to split the combined multiple
subcarriers. According to the OFDM, the complexity of the receiver in a
frequency selective fading environment of a broadband channel can be
reduced and a spectral efficiency can be improved through selective
scheduling in a frequency domain by utilizing different channel
characteristics of subcarriers. The OFDMA is a multiple access scheme
based on the OFDM. According to the OFDMA, different subcarriers can be
allocated to a plurality of users, thereby improving the efficiency of
radio resources.

[0052]There may be various types of control information such as an ACK
(Acknowledgement)/NACK (Negative Acknowledgement) signal indicating
whether or not re-transmission should be performed, a CQI (Channel
Quality Indicator) indicating quality of a downlink channel, a random
access preamble for a random access procedure, and MIMO control
information such as a PMI (Precoding Matrix Index), an RI (Rank
Indicator), etc.

[0053]An orthogonal sequence may be used to transmit control information.
The orthogonal sequence refers to a sequence having good correlation
characteristics. The orthogonal sequence may include, for example, a
CAZAC (Constant Amplitude Zero Auto-Correction) sequence.

[0054]Regarding a ZC (Zadoff-Chu) sequence, one of the CAZAC sequences,
the k-th element c(k) of a root ZC sequence which corresponds to a root
index M may be expressed as shown:

[0057]Equation 2 means that the size of the ZC sequence is always 1, and
Equation 3 means that auto-correlation of the ZC sequence is expressed as
a Dirac-delta function. Here, the auto-correlation is based on circular
correlation. Equation 4 means that cross correlation is always a
constant.

[0058]In the wireless communication system, if it is assumed that cells
are discriminated by the root indexes of the ZC sequence, the user
equipment would need to know a root index or a group of root indexes that
can be used within a cell and the base station should broadcast an
available root index or an available group of root indexes to the user
equipment.

[0059]If the length of the ZC sequence is N, the number of root indexes
would be to the number of relative prime numbers to N among the natural
numbers smaller than N. If N is a prime number, the number of root
indexes would be N-1. In this case, in order for the base station to
inform the user equipment about one of the N-1 number of root indexes,
ceil(log2(N-1)) bits are required. Ceil(x) indicates the smallest
integer greater than x.

[0060]Each cell may use various number of root indexes according to a cell
radius. If the cell radius increases, the number of ZC sequences that can
maintain orthogonality through cyclic shift may be reduced due to an
influence of propagation delay or a round trip delay and/or a delay
spread. Namely, if the cell radius increases, although the length of the
ZC sequence is fixed (regular, uniform), the number of available cyclic
shifts in a corresponding root index may be reduced. Because the
sequences created by the cyclic shifts in the root index have
orthogonality to each other, so they are also called ZCZ (Zero
Correlation Zone) sequences. The minimum number of ZC sequences allocated
to user equipments in each cell should be guaranteed. Thus, if the cell
radius increases, the number of root indexes used in each cell is
increased to secure the minimum number of ZC sequences.

[0061]It is assumed that a group of available root ZC indexes in each cell
is Ri, and the M number of groups of root ZC indexes in all is set. This
can be expressed as R1, R2, . . . , RM. If Ri=10, it
can be said that cells in which Ri is set use 10 root ZC indexes. It is
assumed that N=839, M=7, R1=1, R2=2, R3=4, R4=8,
R5=16, R6=32, and R7=64 according to each cell radius.
Then, if the cell radius is large, minimum 7 bits
(ceil(log2(7))+ceil(log2(838/64))=7 bits) is required to
transmit control information, and if the cell radius is small, maximum 13
bits (ceil(log2(7))+ceil(log2(838/1))=13 bits) are required to
transmit control information.

[0062]As wireless communication systems are advanced, demands for a higher
transfer rate are increasing and cells having a smaller radius are
increasing. Because such cells having a small radius use only a single
root ZC index, more bits are required to transmit control information,
possibly causing a signal overhead. Thus, a technique for reducing the
number of bits required for signaling is necessary in each cell. In
particular, it is important to reduce the number of signaling bits in the
cells having the small cell radius.

[0063]FIG. 3 is a flow chart illustrating the process of a method of
generating sequences according to one exemplary embodiment of the present
invention.

[0064]Referring to FIG. 3, a plurality of root ZC sequences is divided
into one or more subgroups according to a predetermined cyclic shift
parameter (S110). The subgroups include at least one root ZC sequence. If
the cyclic shift parameter is Ncs, a root ZC sequence has zero
correlation zones of length of Ncs-1. The cyclic shift parameter is a
parameter for obtaining a cyclic shift unit of the root ZC sequence, and
the subgroups may be ordered according to the cyclic shift parameter.
Because the Doppler effect is strong in high speed environment, the
cyclic shift unit is obtained by using the cyclic shift parameter
according to each maximum supportable cell radius and a Doppler shift of
detection stage. The cyclic shift unit is a unit for cyclic-shifting the
root ZC sequence. The cyclic shift parameter of the root ZC sequence is
smaller than or equal to the predetermined cyclic shift parameter of the
subgroup of the root ZC sequence. The value of cyclic shift of the root
ZC sequence is greater than the cyclic shift parameter of the root ZC
sequence.

[0065]The root ZC sequences are ordered according to CM (Cubic Metric) in
a subgroup (S120). The ordering of the root ZC sequences according to the
CM characteristics refers to ordering the root ZC sequences according to
the CM characteristics of the ZC sequences according to combination of
the root ZC indexes. As the metric of ordering the root ZC sequences in a
subgroup, cross-correlation, PAPR (Peak-to-Average Power Ratio), a
Doppler frequency, etc, as well as the CM, may be used. The ordering
according to the cross-correlation characteristics refers to ordering the
root ZC sequences according to cross-correlation of ZC sequences
according to combinations of the root ZC indexes. The ordering according
to the PAPR characteristics refers to ordering the root ZC sequences
according to PAPR characteristics of the ZC sequences according to
combinations of the root ZC indexes. The ordering according to the
Doppler frequency characteristics refers to ordering the root ZC
sequences according to a robust degree of the root indexes to the Doppler
frequency.

[0066]A gain can be obtained by using root indexes having a robust Doppler
frequency in a relatively high mobility cell or high speed cell. In case
of using restricted cyclic shifts in a high mobility cell, the root
indexes of root ZC sequences can be ordered (or grouped) according to a
maximum supportable cell radius or a maximum supportable cyclic shift
characteristics. The root indexes of root ZC sequences can be divided
into subgroups by comparing maximum supportable cyclic shift parameters
and predetermined cyclic shift parameters of the respective root ZC
cyclic sequences, whereby root ZC sequences in each subgroup can have
similar characteristics.

[0067]Physical root indexes of root ZC sequences belonging to one subgroup
are mapped to consecutive logical indexes (S130). The physical root
indexes refer to root indexes of ZC sequences which are actually used for
the base station and/or the user equipment to transmit control
information or a random access preamble. The logical indexes refer to
logical root indexes to which the physical root indexes are mapped.

[0068]In case that the root ZC sequences are divided into subgroups
according to the predetermined cyclic shift parameters and the
consecutive logical indexes are allocated in the subgroups as described
above, the base station may inform the user equipment about only at least
one logical index to provide information about a plurality of ZC
sequences having similar characteristics. For example, it is assumed that
the root ZC sequences are ordered in a subgroup according to the CM and a
single logical index is informed to the user equipment. Then, the user
equipment generates root ZC sequences from the physical root indexes to
which the received single logical index is mapped. If the number of ZC
sequences (e.g., the number of available cyclic shifts of the ZC
sequences) generated from the single logical index is insufficient, the
user equipment would generates new root ZC sequences from physical root
indexes mapped to a logical index adjacent to the received logical index.
Because the adjacent (consecutive) logical indexes have the similar CM
characteristics, even if only one logical index is given, the user
equipment can generate a plurality of ZC sequences having the similar CM
characteristics.

Example of Ordering According to CM Characteristics

[0069]FIG. 4 is a graph showing CM (Cubic Metric) characteristics and
maximum supportable cell radius characteristics according to physical
root indexes according to one exemplary embodiment of the present
invention. FIG. 5 is a graph showing the CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to one exemplary embodiment of the present invention. FIG. 6 is
a graph showing the CM characteristics and maximum supportable cell
radius characteristics according to logical root indexes according to
another exemplary embodiment of the present invention.

[0070]If `N` is the length of a ZC sequence, the physical root indexes in
FIG. 4 may be expressed as UP=1, 2, 3, N-3, N-2, N-1. FIG. 5 shows
the results obtained by alternately picking up the physical root indexes
from the start and from the end, one by one, and re-ordering them as
UL=1, N-1, 2, N-2, 3, N-3, 4 . . . . FIG. 6 shows the results
obtained by ordering the physical indexes in FIG. 4 as CM values
corresponding to the logical indexes.

[0071]Table 1 shows an example of CM-based ordering of the physical root
indexes and logical indexes.

[0072]Because the physical root indexes are ordered according to the CM
characteristics and then mapped to the logical indexes, the CM
characteristics of the ZC sequences corresponding to the consecutive
logical indexes can be similarly maintained and a CM-based cell planning
can be possibly performed. The base station may plan the CM-based cell in
a power-limited environment such as in a cell where a channel environment
is not good or in a cell having a large cell radius, etc. In addition,
the base station may use indexes having good CM characteristics as
dedicated preambles for handover or the like. A user equipment in a bad
channel environment already uses its maximum power, so it can hardly
obtain a power ramping effect. Then, the base station can allocate an
index with good CM characteristics to the user equipment to increase a
detection probability.

Example of Ordering According to Maximum Supportable Cell Radius
Characteristics

[0073]FIG. 7 is a graph showing CM characteristics and maximum supportable
cell radius characteristics according to physical root indexes according
to another exemplary embodiment of the present invention. FIG. 8 is a
graph showing CM characteristics and maximum supportable cell radius
characteristics according to logical root indexes according to another
exemplary embodiment of the present invention. FIG. 9 is a graph showing
CM characteristics and maximum supportable cell radius characteristics
according to logical root indexes according to still another exemplary
embodiment of the present invention.

[0074]Referring to FIGS. 7 to 9, FIG. 7 shows the ordering of ZC sequences
used in FIG. 4 according to the maximum supportable cell radius. If `N`
is the length of the ZC sequence, the physical root indexes UP=1, 2,
3, . . . , N-3, N-2, N-1 in FIG. 7 are re-ordered by (1/UP) mod N.
In this case, performing (1/UP) mod N on the ZC sequence indexes
generated in time domain refers to mapping the ZC sequence indexes
generated in the time domain to ZC sequence indexes generated in a
frequency domain. In other words, such conversion refers to reordering
the characteristics of ZC sequence indexes generated in a time domain as
the ZC sequence indexes generated in a frequency domain. FIG. 8 shows the
results obtained by alternately picking up the indexes, which have been
converted from the physical indexes UP into (1/UP) mod N, from
the start and from the end, one by one, and re-ordering them as 1, N-1,
2, N-2, 3, N-3, 4, . . . . FIG. 9 shows the results obtained by
accurately re-ordering according to the maximum supportable cell radius
corresponding to the physical indexes.

[0076]The method of reordering according to the maximum supportable cell
radius can be applicable in case of using restricted cyclic shifts in a
high speed cell environment. In using the restricted cyclic shifts, a
value of a supportable cyclic shift parameter Ncs may vary according to
indexes. If the physical root indexes as shown in FIG. 4 are used as it
is, it may be difficult to use the consecutive physical indexes in a
single cell. Thus, indexes that are not repeated for each cell should be
allocated in an overall network, but this may cause a problem: Reuse
factors of a sequence are reduced to make cell planning difficult. This
problem can be solved by using logical indexes ordered according to the
maximum supportable cell radius characteristics, but such ordering
according to the maximum supportable cell radius characteristics may fail
to obtain a gain in the CM characteristics.

Example of Ordering According to CM Characteristics and Maximum
Supportable Cell Radius Characteristics

[0077]The ordering according to the CM characteristics and the ordering
according to the maximum supportable cell radius characteristics may have
the opposite characteristics. A method for achieving both gains of the CM
characteristics and the maximum supportable cell radius characteristics
will now be described.

[0078]The method of ordering by combining various characteristics follows
the following procedures.

[0079]Step 1. The entire indexes are ordered according to specific
(particular) characteristics.

[0080]Step 2. The entire indexes are divided into sections (or groups)
based on relevant values (grouping).

[0081]Step 3. The indexes of the sections are ordered according to
respective different characteristics in each section (or group).

[0082]Step 4. The steps 2 and 3 are repeated. In this case, in dividing
the indexes into sections, a subsequent section may be associated with a
preceding section, or the subsequent section may not have any relation
with the preceding section and a new rule may be applied to the
subsequent section.

[0083]FIG. 10 is a graph showing CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to still another exemplary embodiment of the present invention.
Namely, FIG. 10 shows ordering according to the maximum supportable cell
radius characteristics and sections of the maximum supportable cell
radius set according to particular values Ncs (predetermined cyclic shift
parameters). FIG. 11 is a graph showing ordering according to CM
characteristics within set sections in FIG. 10.

[0084]Referring to FIGS. 10 and 11, first, the entire indexes are ordered
according to the maximum supportable cell radius and divided into
sections according to the cyclic shift parameters Ncs or the maximum
supportable cell radio values. The cyclic shift parameters Ncs are to
obtain a cyclic shift unit supported per ZC sequence.

[0086]If the physical indexes have such characteristics as shown in FIG.
4, the entire indexes can be ordered according to the maximum supportable
cell radius as shown in FIG. 9. When the sections are divided by the
maximum supportable cell radius value with respect to the cyclic shift
parameters Ncs, results as shown in FIG. 10 are obtained. Here, the
values `No guard sample` were used.

[0087]When the root indexes are ordered according to the CM
characteristics in each divided section, results as shown in FIG. 11 are
obtained. In this case, hybrid ordering that considers both the CM and
the maximum supportable cell radius is applied to the mapping from the
physical indexes to the logical indexes as shown in Table 4.

[0088]A plurality of sequences are divided into a plurality of sub-groups
according to predetermined cyclic shift parameters Ncs, and ordered
according to CM characteristics in each sub-group. The plurality of
sub-groups may be ordered according to each corresponding cyclic shift
parameter. The biggest peaks (or the smallest peaks) appearing at upper
portions in the graph as shown in FIG. 11 indicate root indexes having a
maximum CM (or a minimum CM) in each sub-group.

[0089]Each cell may use the consecutive logical indexes through the hybrid
ordering according to the cyclic shift parameters and the CM
characteristics regardless of a cell size, and CM-based cell planning can
be possible according to characteristics of each cell. The base station
may use the smallest logical index allocated to the base station itself
for the user equipment in a particular power restricted environment in
each cell. For example, the base station may use the smallest logical
index as a dedicated preamble for a user equipment that performs
handover. In the smallest cell size interval, a supportable cell size is
very small and an index having a value smaller than 0 km may exist. Such
index indicates an index that cannot use the restricted cyclic shift. In
addition, the sections may be further divided for a simply index
allocation. In FIG. 11, the first section is divided by 0˜1.1 km,
but the section may be divided into smaller parts and ordered on the
basis of the CM. For example, the first section may be divided into two
parts of 0˜500 m and 500 m˜1.1 km and can be ordered on the
basis of the CM.

[0091]Table 5 shows that a plurality of physical root indexes are divided
into a plurality of sub-groups according to predetermined cyclic shift
parameters Ncs and consecutive logical indexes are allocated in each
sub-group.

[0092]With such logical indexes set, a sequence can be easily selected
according to a cell size in a high mobility cell. In addition, if a cell
requires low CM characteristics, it may simply select front indexes among
indexes that may be used in its cell size to thus use indexes having low
CM characteristics. Table 5 does not mean that only the index values
(physical indexes or logical indexes) related to the Ncs are used. An
index, which may be suitable for the CM characteristics of a cell, may be
selectively used regardless of a cell size in a low/middle mobility cell.
In addition, An Ncs section table that can be used in the low/middle
mobility cell may be separately set. In this case, a table to be applied
by using a discrimination signal of a cell having the low/middle mobility
cell and a cell having the high mobility cell may be selected.

[0093]FIG. 12 is a graph showing CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to yet another exemplary embodiment of the present invention.
Namely, FIG. 12 shows ordering based on the plurality of characteristics
and pair allocation.

[0094]Referring to FIG. 12, ZC sequences have complex conjugate symmetry
characteristics, based on which indexes having the complex conjugate
symmetry can be pair-allocated consecutively.

[0095]The complex conjugate symmetry of the ZC sequences can be expressed
as shown

xu=a(k)=x*u=N-a(k) [Equation 5]

[0096]where (.)* indicates complex conjugate. The sum of two root indexes
of two ZC sequences having complex conjugate symmetry is equal to the
length of a ZC sequence. If only a single root index is used in a cell,
such characteristics cannot be obtained, but in case of using a plurality
of root indexes having complex conjugate symmetry characteristics,
complexity of a detector of a receiver can be reduced to a half. The root
indexes having complex conjugate symmetry characteristics can be
consecutively allocated while applying the CM-based ordering, the maximum
supportable cell radius-based ordering and the hybrid ordering, etc.
thereto. When the indexes are pair-allocated, the base station signals
only a single logical index and the user equipment naturally uses pair
indexes while increasing the logical indexes as necessary.

[0097]In the above Table 5, each group includes the odd number of indexes,
and in order to constitute the complex conjugate symmetry
characteristics, one index of a higher group may be used by a lower
group. This can be expressed as shown in Table 6.

[0098]The results of constituting the complex conjugate symmetry
characteristics appear to be similar to those of hybrid ordering in FIG.
11. Namely, the indexes can be ordered such that they can be
pair-allocated without degrading particular characteristics of them.

[0099]FIG. 13 is a graph showing CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to another exemplary embodiment of the present invention.
Namely, FIG. 13 shows ordering based on the plurality of characteristics
and pair allocation.

[0100]Referring to FIG. 13, the sections divided in FIG. 12 can be more
minutely divided. For example, the sections of the configuration numbers
11 and 12 in Table 3 can be halved to use a wider maximum cell radius.

[0101]Table 7 is a mapping table showing physical indexes of respective
sections when the 11-th and 12-th sections are halved.

[0102]The maximum cell radius can be increased from 29.14 km to 34.15 km
so as to be used by applying Table 7. Here, particular sections are
halved and re-ordered, but it is merely an example. That is, the size of
particular sections can be divided in various manners. For example, in
order to support a particular maximum cell radius, sections may be
divided based on the particular maximum cell radius. Alternatively,
sections may be divided such that the number of indexes used in a
particular section is doubled. Sections having a small number of indexes
can be grouped into one section, to which the second ordering may be
applied. In addition, a section having a large number of indexes can be
divided into two (or more) sections, to which the second ordering may be
applied.

[0103]FIG. 14 is a graph showing CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to another exemplary embodiment of the present invention.
Namely, FIG. 13 shows that indexes are divided into groups based on the
CM characteristics and are ordered according to a maximum supportable
cell size in each group.

[0104]Referring to FIG. 14, first, the indexes may be ordered according to
the CM characteristics, divided into a group having a CM higher than 1.2
dB, namely, a QPSK CM, and a group having a lower CM, and then ordered
according to the maximum supportable cell radius in each group. The
indexes in the group having the CM lower than QPSK may be ordered
according to the order that the maximum supportable cell size is reduced,
and the indexes in the group having the CM higher than QPSK may be
ordered in the order that the maximum supportable cell size is increased.

[0105]Table 8 is a mapping table of physical indexes by section in case
where the indexes are ordered according to the CM characteristics,
divided into groups based on 1.2 dB, a single CM value, and then ordered
according to the maximum supportable cell size in each group.

[0107]FIG. 15 is a graph showing the number of restricted cyclic shifts
available per logical index according to an Ncs with respect to CM
mapping according to one exemplary embodiment of the present invention.
FIG. 16 is a graph showing the number of restricted cyclic shifts
available per logical index according to the Ncs with respect to maximum
supportable cell size mapping according to one exemplary embodiment of
the present invention. FIG. 17 is a graph showing the number of
restricted cyclic shifts available per logical index according to the Ncs
with respect to hybrid mapping according to one exemplary embodiment of
the present invention.

[0108]Referring to FIGS. 15 to 17, compared with the CM mapping, the
maximum supportable cell size mapping and the hybrid mapping may use
consecutive indexes in a high speed cell. For example, it is assumed that
there are twenty cells, the cyclic shift parameter Ncs of a first cell is
13, the Ncs of the subsequent two cells (i.e., second and third cells)
are 26, those of the subsequent three cells are 38, those of the
subsequent four cells are 38, those of the subsequent four cells are 52,
and those of the subsequent four cells are 64. In this case, pair index
allocation is applied to each mapping. The Ncs indicates the number of
cyclic shifts according to cell sizes. Referring to FIG. 13, it is noted
that a middle portion is 0 and any available restricted cyclic shift does
not appear. On the contrary, Referring to FIGS. 15 and 16, any available
restricted cyclic shift does not appear. Namely, the consecutive indexes
cannot be used in the CM mapping but can be used in the maximum
supportable cell size mapping and hybrid mapping.

[0109]FIG. 18 is a graph showing examples of logical root indexes
allocated to cells with respect to the CM mapping according to one
exemplary embodiment of the present invention. FIG. 19 is a graph showing
examples of logical root indexes allocated to cells with respect to the
maximum supportable cell size mapping according to one exemplary
embodiment of the present invention. FIG. 20 is a graph showing examples
of logical root indexes allocated to cells with respect to the maximum
supportable cell size mapping according to one exemplary embodiment of
the present invention. Namely, FIGS. 18 to 20 show which indexes are
allocated to cells based on the assumption in FIGS. 15 to 17.

[0110]Referring to FIGS. 18 to 20, it is assumed that every cell has high
speed mobility. Referring to FIG. 18, it is noted that consecutive
indexes are not used in a large cell. In comparison, Referring to FIGS.
19 and 20, it is noted that consecutive indexes can be used in a large
cell. In FIGS. 19 and 20, if a cell has the Ncs of 209 (Ncs=209), four
cells having the Ncs of 167 (Ncs=167) can be constructed. The reason is
because, in FIG. 18, consecutive indexes cannot be used. More
importantly, in FIG. 18, it is noted that, if a cell has the Ncs of 209
and three cells have the Ncs of 167, any of cells having NCS=139,
Ncs=104, Ncs=83, and Ncs=76 cannot be constructed. In comparison, in
FIGS. 19 and 20, cells of various sizes can be constructed. Also, in FIG.
18, it is noted that a plurality of indexes has a value 0 at the y axis
and are not used in a high mobility cell. If those indexes can be used
when the high mobility cell is mixed with only a low mobility cell, but
such indexes drastically degrade the cell construction capabilities.
Thus, failing to use the consecutive indexes much degrades the re-use
factor when a plurality of large cells exists. That is, by using the
consecutive indexes, a different cell may use an extra space. The use of
the consecutive indexes may not make much difference in a network
including only small cells, but as far as a network including a plurality
of large cells concerned, the support of the use of the consecutive
indexes can increase the re-use factor. FIGS. 18 to 20 consider the case
where every cell has high speed mobility, but even in a case where cells
having low speed mobility or middle speed mobility exist, the re-use
factor is restricted if the consecutive indexes are not used for the same
reasons. Also, if the consecutive indexes are used in a cell having low
speed mobility or middle speed mobility, the re-use factor of the cell
having high speed mobility is further restricted.

[0111]The accurate indexes of each mapping as used are as shown in Table
9, Table 10, and Table 11. Table 9 shows the indexes used for the CM
mapping, Table 10 shows indexes used for the maximum support cell size
mapping, and Table 11 shows the indexes used for the hybrid mapping. In
Table 9 and Table 10, physical root indexes with respect to logical
indexes 1 to 838 are arranged in sequence.

[0113]FIG. 21 is a view illustrating a method of searching logical root
indexes according to the CM characteristics according to one exemplary
embodiment of the present invention. FIG. 22 is a view illustrating a
method of searching logical root indexes according to the CM
characteristics according to another exemplary embodiment of the present
invention. FIG. 23 is a view illustrating a method of searching logical
root indexes according to the CM characteristics according to still
another exemplary embodiment of the present invention.

[0114]Referring to FIGS. 21 to 23, the physical indexes are first ordered
according to a supportable cell size. Thereafter, a method of using
available indexes in each cell vary according to characteristics of a
single transmitted index. Allocation of logical indexes may be formed
according to one logical index+Ncs. It can be performed by the following
two methods.

[0115]In one method, each cell uses only a single sequence class (See FIG.
20). It is divided into a low CM index and a high CM index.

[0116]If a transmitted logical index has CM characteristics which are
lower than or the same as the QPSK CM (1.2 dB) of the SC-FDMA, the
closest adjacent logical indexes having the CM characteristics which are
lower than or the same as the QPSK CM of the SC-FDMA are searched and
used in sequence. If a transmitted logical index has CM characteristics
which are higher than the QPSK CM of the SC-FDMA, the closest adjacent
logical indexes having the CM characteristics which are higher than the
QPSK CM of the SC-FDMA are searched and used in sequence.

[0117]In another method, a single cell may use either sequence class
(lower CM or higher CM) (See FIGS. 20 and 21). It is divided into a lower
CM index, a higher CM index and a mixed CM index.

[0118]If a transmitted logical index has CM characteristics which are
lower than or the same as the QPSK CM (1.2 dB) of the SC-FDMA, the
closest adjacent logical indexes having the CM characteristics which are
lower than or the same as the QPSK CM of the SC-FDMA are searched and
used in sequence. In this case, when it reaches the end of an Ncs
segment, the index is reset as an index having a first higher CM of a
next Ncs segment. If a transmitted logical index has CM characteristics
which are higher than the QPSK CM (1.2 dB) of the SC-FDMA, the closest
adjacent logical indexes having the CM characteristics which are higher
than the QPSK CM of the SC-FDMA are searched and used in sequence. In
this case, if it reaches the end of an Ncs segment, the index is reset as
an index having a first lower CM of a next Ncs segment.

[0119]The directions (+/-, direction in which indexes are
increased/decreased) for searching indexes having the same
characteristics may be the same or different. The direction for searching
indexes does not affect the proposed technique, like the ordering
direction (ascent/descent) of indexes as mentioned above.

[0120]FIG. 24 is a graph showing CM characteristics according to physical
root indexes according to one exemplary embodiment of the present
invention.

[0121]Referring to FIG. 24, the sequence class may be defined according to
physical indexes. The physical root indexes may be classified by setting
a CM classification threshold value. The classification of the physical
root indexes may be simply performed by checking whether or not a
selected physical index belongs to a high CM region or a low CM region.
For example, it can be noted that, if a CM classification threshold value
is 1.2 dB, a high CM region may be determined as [238, NZC-238]. The
use of such method allows generation of indexes through a simple
numerical formula to order the indexes (or index mapping) without the
necessity of a complicated table.

[0122]Mapping to a physical index uphy(ulog) in response to a
logical index ulog based on the maximum supportable cell size (or
Ncs) can be expressed as shown

where, ulog++ indicates the next logical indexes (e.g., ulog+1,
ulog+2, ulog+3, . . . ) associated with ulog and
It=238. In this case, all the indexes are searched in a positive (+)
direction (namely, in a direction that indexes increase). If a mixed CM
index is not allowed, a searching procedure is simple. When a low CM
sequence reaches a boundary of NZC-1 through the ulog++
procedure, it is set with a first logical index of ulog++. If,
however, the mixed CM index is allowed, some conditions are necessary. If
ulog++ reaches a boundary of an Ncs sequence, it is reset with a
first logical index in a ulog++ Ncs segment. If ulog++ reaches
a boundary of the Ncs segment in the ulog++ process for a higher CM,
ulog++ is reset with a first logical index of a next Ncs segment. In
this case, as for the CM characteristics when ulog++ is reset, if
the mixed CM index is not allowed, ulog++ can be reset with a first
index having the same characteristics as those of a transmitted index,
and if the mixed CM index is allowed, ulog++ can be reset with a
higher CM or a lower CM which has been previously determined according to
the characteristics of a transmitted index.

[0125]Another example of selecting an adjacent available index when a
plurality of indexes are used in a cell can be expressed as shown

[0126]where, ulog++ indicates the next logical indexes (e.g.,
ulog+1, ulog+2, ulog+3, . . . ) associated with ulog
and It=238. In this case, indexes are searched in positive (+) and
negative (-) directions (namely, in a direction that indexes increase or
decrease).

[0127]If it is difficult to express the ordering of indexes in numerical
formula, each base station and each user equipment should have a large
ordering table of 838*10 bits (1˜838)=8,380 bits. However, if
Equation 6 is given, each base station and each user equipment can use
the maximum supportable cell size ordering without such an ordering
table. Table 12 shows mapping from physical indexes to logical indexes
based on the maximum supportable cell size using Equation 6.

[0128]In all the exemplary embodiments as described above, when indexes
are ordered based on certain characteristics, the order of values having
the same characteristics does not affect the order of ordering. Also, the
order of pair indexes does not affect the order of ordering. In the
ordering (mapping) method according to all the exemplary embodiments, as
the indexes increase, they are ordered in an ascending order that the CM
or the maximum supportable cell size increases, but it is merely an
example. That is, as the indexes increase, they may be ordered in the
ascending order that the CM or the maximum supportable cell size is
increased or in a descending order that the CM or the maximum supportable
cell size is decreased in each group. In addition, the indexes may be
ordered in the shape of a mountaintop ( ) or in the shape of a mountain
valley (v). And, the directionality of the CM or the maximum supportable
cell size can be determined to be different in each group.

[0129]FIG. 25 is a graph showing CM characteristics and maximum
supportable cell radius characteristics according to logical root indexes
according to another exemplary embodiment of the present invention. As
the logical indexes increase, they may be ordered in the ascending order
that the maximum supportable cell size increases and in the descending
order that the CM decreases. FIG. 26 is a graph showing the CM
characteristics and the maximum supportable cell radius characteristics
according to logical root indexes according to another exemplary
embodiment of the present invention. Respective CM groups have been
grouped based on the cyclic shift parameter Ncs. As the logical indexes
increase, they are ordered in the ascending order that the maximum
supportable cell radius size increases, in the descending order that the
odd number groups of the CM decrease, and in the ascending order that the
even number groups of the CM increase.

[0130]Referring to FIGS. 25 and 26, the directionality of the CM or the
maximum supportable cell size may be determined to be different in each
group. After the indexes are ordered in the ascending order that the
maximum supportable cell size increases, when the indexes are ordered in
the descending order that the CM decreases, the results appear as shown
in FIG. 25. When the odd number groups are ordered in the descending
order that the CM decreases and the even number groups are ordered in the
ascending order that the CM increases, the results appear as shown in
FIG. 26. By making the ordering in adjacent (consecutive) groups
different, a larger number of adjacent (consecutive) indexes having low
CM can be used in a low mobility cell regardless of the maximum
supportable cell radius.

[0131]In all the exemplary embodiments as described above, if a single
index is allocated in each cell in the ordering (mapping) method, each
user equipment may use indexes by adding 1 to or subtracting 1 from a
transmitted index, namely, by increasing or decreasing 1 at a time as
necessary in order to meet the required number of random access preambles
per cell. In case of using indexes by adding 1 at a time, when the
largest index 838 is used, it may return to the smallest index 1 to use
it. In case of using indexes by subtracting 1 at a time, when the
smallest index 1 is used, it may return to the largest index 838 to use
it. In addition, the ascending direction (+/-) may be used differently
according to each characteristics (e.g., a lower CM/a higher CM). When
the indexes are ordered in the ascending direction that the maximum
supportable cell size increases as the indexes increase, because
available indexes are limited in a large cell, it would be preferred to
allocate indexes starting from a large cell. In this case, the simplest
method of cell planning is to allocate the largest index to the largest
cell and then use indexes by stages by subtracting 1 at a time.

Embodiment of Hybrid Ordering

[0132]FIG. 27 is a graph showing a process of grouping CM ordering into
two groups. FIG. 28 is a graph showing a process of grouping indexes
ordered according to maximum supportable Ncs characteristics into Ncs
groups in each group. FIG. 29 is a graph showing a process of ordering
indexes according to the CM characteristics in each Ncs group.

[0133]Referring to FIGS. 27 to 29, (1) the indexes are ordered according
to the CM characteristics. The indexes are divided into a group higher
than 1.2 dB, the QPSK CM of the SC-FDMA, and a group lower than 1.2 dB as
shown in FIG. 27.

[0134](2) After the entire indexes are ordered according to the maximum
cell radius, they are divided into sections according to the Ncs value
(or the maximum supportable cell radius value). After the respective
groups are ordered according to the maximum supportable cell radius, they
are divided into sections with a maximum supportable cell radius value
with respect to the Ncs. In this case, the groups may be all divided into
different groups according to the Ncs value, several particular Ncs
values can be divisionally grouped, or a particular Ncs value can be
further divided. Here, the case of using the groups corresponding to
every Ncs value is used, and the divided sections are as shown in FIG.
28.

[0135](3) The indexes are ordered according to the CM characteristics in
each divided section as shown in FIG. 29. Here, as the Ncs sample values,
13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 119, 167, 237, 279, and 419 were
used. Table 13 shows the relationship between the physical indexes and
the logical indexes according to the results of FIG. 29.

[0136]In Table 13, there are groups having only a smaller number of
indexes. Such groups having only a smaller number of indexes may be
united with an adjacent group to constitute a single group.

[0137]In all the exemplary embodiments as described above, in case of pair
allocation, relative positions of two adjacent pair indexes do not affect
the proposed technique. In addition, when the indexes are ordered
according to certain characteristics (e.g., the CM, the maximum
supportable cell size (or Ncs, etc.)), the order of indexes having
similar characteristics does not affect the proposed technique.

[0138]In use the above-described method, the user equipment and the base
station should have a mapping table showing the relationship between the
physical indexes and the logical indexes in each memory. In this case,
the entire 838 indexes may be stored in each memory or only a half of
them may be stored according to pair allocation. If only the half is
stored, it may be assumed that (N-i)-th index is present after the i-th
index, for processing.

[0139]When the indexes are ordered by using the above-described method and
indexes available in a cell are informed to the base station, a method of
informing about the number of Ncs configurations and a single logical
index may be used. In this case, a single logical index can be informed
by logical indexes 1 to 838 by using 10 bits. Alternatively, indexes 1 to
419 may be informed by using only one value of pair allocation with 9
bits. In this case, for the separate use of the pair allocation, an
additional 1 bit may be used to indicate whether the used indexes are the
front indexes 1 to 419 or the rear indexes 420 to 838 in the pair
allocation. When indexes are informed with only 9 bits, they can be
processed on the assumption that the (N-i)-th index follows the i-th
index.

[0140]FIG. 30 is a flow chart illustrating the random access procedure
according to one exemplary embodiment of the present invention.

[0141]Referring to FIG. 30, a user equipment (UE) receives random access
information from the base station (BS) (S310). The random access
information includes information about a cyclic shift parameter Ncs and
information about generation of a plurality of random access preambles.
The cyclic shift parameter Ncs is used to obtain the value of cyclic
shift of a root ZC sequence. The information about generation of a random
access preamble is information regarding a logical index. The logical
index is an index to which a physical root index of a root ZC sequence is
mapped. The logical index becomes a source index for generating a set of
random access preambles.

[0142]The information about the cyclic shift parameter Ncs and the logical
index may be broadcasted as part of system information or transmitted on
a downlink control channel. The method or format of transmitting the
cyclic shift parameter Ncs or the logical index is not limited.

[0143]The user equipment acquires mapped physical root indexes from the
logical index (S320). There are 64 preambles available in each cell. The
set of 64 preamble sequences in a cell is found by including first, in
the order of increasing cyclic shift, all the available cyclic shifts of
a root Zadoff-Chu sequence with the logical index. Additional preamble
sequences, in case 64 random access preambles cannot be generated from a
single root Zadoff-Chu sequence, are obtained from the root sequences
with the consecutive logical indexes until all the 64 sequences are
found. The logical root sequence order is cyclic: the logical index 0 is
consecutive to 837 when Nzc=838. Thus, the user equipment can find every
available random access preamble through the single logical index.

[0144]Even if the base station informs the user equipment about only a
single logical index, the user equipment can find the available 64 random
access preambles. In addition, the root ZC sequences corresponding to the
consecutive logical indexes have similar characteristics, all the
generated sequences have substantially similar characteristics. Also, the
root ZC sequences corresponding to the consecutive logical indexes may
have complex conjugate symmetry which means the sum of two root index of
the root ZC sequences corresponding to the two consecutive logical
indexes is equal to the length of a root ZC sequence.

[0145]The logical indexes can be mapped to the physical root indexes of
the root ZC sequence in sequence, after the physical root indexes are
ordered according to the CM by subgroup. The subgroups have been obtained
by grouping the ZC sequences by the predetermined cyclic shift parameter.
Even if a consecutive logical index is selected, root ZC sequences having
similar characteristics as those of the existing logical index can be
obtained. Thus, only with a single logical index, the user equipment can
acquire the 64 preamble sequences required for selecting the random
access preamble.

[0146]As mentioned above, the logical index is the index to which the
physical indexes are mapped in a state that the ZC sequences have been
grouped into subgroups according to the predetermined cyclic shift
parameter and ordered by the CM in each subgroup. Thus, the logical
sequences belonging to a single subgroup have the same cyclic shift
parameter. Although the base station allocates only the logical sequences
in consideration of mobility of the user equipment, the user equipment
can acquire the plurality of ZC sequences having the same cyclic shift
parameter Ncs and similar CM characteristics.

[0147]The user equipment transmits a selected random access preamble to
the base station on the RACH (Random Access Channel) (S330). That is, the
user equipment randomly selects one of the 64 available random access
preambles and transmits the selected random access preamble.

[0148]The base station transmits a random access response, a response to
the random access preamble (S340). The random access response may be a
MAC message configured in a MAC, a higher layer of a physical layer. The
random access response is transmitted on a DL-SCH (Downlink Shared
Channel). The random access response is addressed by an RA-RNTI (Random
Access-Radio Network Temporary Identifier) transmitted on a PDCCH
(Physical Downlink Control Channel). The RA-RNTI is a identifier to
identify the used time/frequency resource for random access. The random
access response may include timing alignment information, an initial
uplink grant, and a temporary C-RNTI (Cell-Radio Network Temporary
Identifier). The timing alignment information is timing correction
information for uplink transmission. The initial uplink grant is ACK/NACK
information with respect to the uplink transmission. The temporary C-RNTI
refers to a user equipment's identifier that may not be permanent until
collision is resolved.

[0149]The user equipment performs scheduled uplink transmission on a
UL-SCH (S350). If there is data to be transmitted additionally as
necessary, the user equipment performs uplink transmission to the base
station and performs a collision settlement procedure.

[0150]If an error occurs in the transmission of the random access
preamble, the random access procedure is delayed. Since the random access
procedure is performed at an initial access to the base station or in a
handover process to the base station, the delay of the random access
procedure may cause an access delay or a service delay. A user equipment
can obtain 64 preamble sequences suitable for the high speed environment,
whereby the user equipment can reliably transmit the random access
preamble in the high speed environment.

[0151]By using consecutive logical indexes, a set of random access
preambles having similar physical characteristics can be generated.
Control signaling to generate random access preambles can be minimized.
Random access failure can be reduced under high speed environment and
efficient cell planning can be performed.

[0152]FIG. 31 is a schematic block diagram of elements of a user equipment
to which the exemplary embodiments are applied.

[0153]A user equipment 50 may include a processor 51, a memory 52, an RF
unit 53, a display unit 54, and a user interface unit 55. The processor
51 may handle generation and mapping of sequences and implement functions
regarding the various exemplary embodiments as described above. The
memory 52 may be connected to the processor 51 and store an operating
system, applications and files. The display unit 54 may display various
information and use the known elements such as an LCD (Liquid Crystal
Display), OLEDs (Organic Light Emitting Diodes), etc. The user interface
unit 55 may be formed by combining user interfaces such as a keypad, a
touch screen, or the like. The RF unit 53 is coupled to the processor 51
and transmits or receives radio signals.

[0154]Every function as described above can be performed by a processor
such as a microprocessor based on software coded to perform such
function, a program code, etc., a controller, a micro-controller, an ASIC
(Application Specific Integrated Circuit), or the like. Planning,
developing and implementing such codes may be obvious for the skilled
person in the art based on the description of the present invention.

[0155]Although the embodiments of the present invention have been
disclosed for illustrative purposes, those skilled in the art will
appreciate that various modifications, additions and substitutions are
possible, without departing from the scope of the invention. Accordingly,
the embodiments of the present invention are not limited to the
above-described embodiments but are defined by the claims which follow,
along with their full scope of equivalents.